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Thermochemistry

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Glauber's salt, sodium sulfate decahydrate (Na2SO4 * 10H2O) undergoes a phase transition (that is melting or freezing) at a convenient temp of 32 degrees C

Na2SO4 * 1o H2O(s) yields Na2SO4 * 10 H2O(l) Change H = 74.4 kJ/mol

As a result this compound is used to regulate the temperature in homes. It is placed in plastic bags in the ceiling of a room. During the day, the endothermic melting process absorbs heat from the surroundings, cooling the room. At night, it gives off heat as it freezes. Calculate the mass of Glauber's salt in kilograms needed to lower the temperature of air in a room by 8.2 degrees C at 1.0atm. The dimensions of the room are 2.8m*10.6m*17.6m, the specific heat of air is 1.2 J/g C, and the molar mass of air may be taken as 29.0g/mol.

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Solution Preview

Volume of room = 2.8m*10.6m*17.6m = 522.4 (m3)
Density of air = 1.168 kg/m3
Mass of air in room = ...

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Neutralization Reaction in Thermochemistry

A quantity of 2 x 102 mL of 0.862 Molar HCl is mixed with 2 x 102 mL of 0.431Molar Ba(OH)2 in a constant pressure calorimeter that has a heat capacity of 453 J/oC.

The initial temperature of the HCl and Ba(OH)2 solutions is the same at 20.48oC. For the process

H+(aq) + OH-(aq) --> H2O(L)

the heat of neutralization is -56.2 KJ.

What is the final temperature of the mixed solution?

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